The present invention relates to a control apparatus for controlling the amount of air which is sucked into an internal combustion engine in accordance with the operation state of the engine and, more particularly, to means for controlling the amount of air flowing through a bypass air passageway, which is arranged in parallel to an intake pipe, to allow the intake air of an internal combustion engine to pass.
A throttle valve, which is driven and controlled by an accelerator pedal, is set in the intake pipe for feeding air into an internal combustion engine. The amount of intake air into an internal combustion engine is controlled by the opening state of that throttle valve. On one hand, in the idle state where the foregoing throttle valve portion is bypassed and the throttle valve is controlled so as to be closed, the intake air into the internal combustion engine is supplied through the foregoing bypass air passageway.
In this case, an air amount control valve as shown in, for instance, Japanese Patent Application Laid-Open No. 126534/1982 is set in the bypass air passageway and the amount of intake air into the internal combustion engine is controlled by this control valve.
When an internal combustion engine is idling, a feedback control is executed such that its rotating speed is set to a preset idle objective rotating speed. This objective rotating speed is set due to the temperature of the cooling water for the engine or the like. Namely, the opening of the air amount control valve provided in the bypass air passageway is feedback controlled to control the amount of intake air so that the engine is rotated and controlled at that objective rotating speed.
The control state of the air amount control valve includes the feedback loop control, whereby the rotating speed of the engine is controlled to become the objective rotating speed and the open loop control whereby such a control is not executed. Either one of those control states is selected in accordance with the operating state of the engine. In this case, when the control state is switched from the open loop control to the feedback loop control, it is necessary to set the control amount in the open loop control state so that the rotating speed of the engine smoothly reaches its objective rotating speed. Therefore, the feedback control amount which varies due to a time change in engine friction, choke of the air passageway, or the like is learned and this learned control amount is reflected to the open loop control.
As the control valve for controlling the amount of intake air, an electromagnetic valve mechanism of the linear solenoid type which can variably control a cross sectional area of the air passageway (by way of the control of its current), is used. The current which is supplied to an exciting coil of this control valve is constituted by, for example, a pulse-like signal due to a square wave, which is generated at every specific period T.sub.0 as shown in FIG. 1A. Its current is set by an effective time width of the square wave signal, namely, duty ratio. The amount of air which passes is variably controlled due to the foregoing current.
Practically speaking, for the control currents of duties as shown respectively by a solid line and a broken line in FIG. 1A, their respective mean currents Im1 and Im2 are as shown by a solid line and a broken line in FIG. 1B. The relation between this mean current Im and the air flow rate which is controlled is as shown in FIG. 1C.
However, this mean current Im varies in accordance to the magnitude of the duty ratio, as mentioned above, and the temperature of the exciting coil for driving the air control valve. Practically speaking, even in the case of a pulse-like control current which is set to the same duty ratio, if the temperature of the foregoing coil is low, an electrical resistance value of this coil is small, so that its mean current value becomes large. On the contrary, when the coil temperature is high, its electrical resistance value is large and its mean current value is small.
Therefore, if one desires to determine the amount of intake air into an internal combustion engine due to the learning control by use of such an air flow rate control valve, the control amount in the learned feedback control state does not always become the amount which was set in correspondence to the foregoing time change, and the control amount in the open loop control state does not become the proper amount.